LeetCode Unique Word Abbreviation

原题链接在这里：https://leetcode.com/problems/unique-word-abbreviation/

题目：

An abbreviation of a word follows the form <first letter><number><last letter>. Below are some examples of word abbreviations:

a) it                      --> it    (no abbreviation)

     1
b) d|o|g                   --> d1g

              1    1  1
     1---5----0----5--8
c) i|nternationalizatio|n  --> i18n

              1
     1---5----0
d) l|ocalizatio|n          --> l10n

Assume you have a dictionary and given a word, find whether its abbreviation is unique in the dictionary. A word's abbreviation is unique if no other word from the dictionary has the same abbreviation.

Example: 

Given dictionary = [ "deer", "door", "cake", "card" ]

isUnique("dear") -> false
isUnique("cart") -> true
isUnique("cane") -> false
isUnique("make") -> true

题解：

把dictionary 变成HashMap<String, HashSet<String>>, key 是 abbr. value 是所有这个缩写原有词的set.

isUnique函数若是对于长度小于3的word return true. 若是HashMap没有word abbr这个key 或者 对应set只有 word这一个词也返回true.

Time Complexity: constructor O(n), n是dictionary长度. isUnique O(1). Space: O(n).

AC Java:

public class ValidWordAbbr {
    HashMap<String, HashSet<String>> hm;
    public ValidWordAbbr(String[] dictionary) {
        hm = new HashMap<String, HashSet<String>>();
        for(String s : dictionary){
            String abbr = getAbbr(s);
            if(!hm.containsKey(abbr)){
                HashSet<String> hs = new HashSet<String>();
                hs.add(s);
                hm.put(abbr, hs);
            }else{
                hm.get(abbr).add(s);
            }
        }
    }

    public boolean isUnique(String word) {
        if(hm.size() == 0 || word.length() < 3){
            return true;
        }
        String abbr = getAbbr(word);
        if(!hm.containsKey(abbr) || (hm.get(abbr).contains(word) && hm.get(abbr).size() == 1)){
            return true;
        }
        return false;
    }
    
    private String getAbbr(String s){
        if(s == null || s.length() < 3){
            return s;
        }
        return s.substring(0,1) + String.valueOf(s.length()-2) + s.substring(s.length()-1);
    }
}


// Your ValidWordAbbr object will be instantiated and called as such:
// ValidWordAbbr vwa = new ValidWordAbbr(dictionary);
// vwa.isUnique("Word");
// vwa.isUnique("anotherWord");